Master-slave-type control system with stand-by suspending control station

Abstract

In a master-slave-type control system, a normal supervisory control station which is a master device, control terminal devices, and a stand-by supervisory control station which is a slave device for effecting an operation of the normal supervisory control station in place thereof are connected with a common transmission passage. The normal supervisory control station receives data from each control terminal device repeatedly sent on the transmission passage to the normal supervisory control station, collects the data from each control terminal device, and sends its internal data on the transmission passage to an imaginary station at the end of each period of data collection. The stand-by supervisory station intercepts the data of each control terminal device repeatedly send on the transmission passage to the normal supervisory control station, collects the data from each control terminal device, and intercepts the data sent from the normal supervisory control station on the transmission passage to the imaginary station at the end of each period of data collection, whereby switching from control by the normal supervisory control station to control by the stand-by supervisory control station is carried out.

What is claimed is: 
     
       1. A master-slave-type control system, comprising: a common transmission passage for transmitting various data;   at least one control terminal device connected to said transmission passage for sending first data repeatedly on said transmission passage;   a normal supervisory control station, connected to said transmission passage, for collecting said first data sent to said transmission passage from each said control terminal device for sending predetermined second data to an imaginary station on said transmission passage; and   a stand-by supervisory control station, connected with said control terminal device and said normal supervisory control station only through said transmission passage, for collecting said first data by intercepting said first data sent on said transmission passage from each said control terminal device and for detecting an abnormality of said normal supervisory control station in accordance with said second data obtained by intercepting said second data sent to said imaginary station on said transmission passage from said normal supervisory control station;   wherein said first data concerns information to be communicated between said control terminal device and a currently operative one of said normal supervisory control station and said stand-by supervisory control station which is currently supervising operation of each said control terminal device, while said second data concerns information on an internal state of said normal supervisory control station; and   wherein said stations carry out switching from control by said normal supervisory control station to control by said stand-by supervisory control station when said abnormality of said normal supervisory control station is detected by said stand-by supervisory control station.   
     
     
       2. The master-slave-type control system according to claim 1, wherein said stand-by supervisory control station detects said abnormality of said normal supervisory control station as nonexistence of said second data normally sent to said imaginary station on said transmission passage from said normal supervisory control station.   
     
     
       3. The master-slave-type control system according to claim 1, wherein when said stand-by supervisory control station detects said abnormality of said normal supervisory control station, said normal supervisory control station carries out switching from control by said normal supervisory control station to control by said stand-by supervisory control station.   
     
     
       4. The master-slave-type control system according to claim 1, wherein when said stand-by supervisory control station detects said abnormality of said normal supervisory control station, said stand-by supervisory control station sends a request signal for promotion to normal station status to said normal supervisory control station through said transmission passage, said normal supervisory control station sends a permission signal to said stand-by supervisory control station through said transmission passage, in response to said request signal for promotion, for promoting said stand-by supervisory control station to said normal station status, and, when said stand-by supervisory control station receives said permission signal, said stand-by supervisory control station takes over operation as a normal supervisory control station in accordance with said first data collected by intercepting said first data, and said normal supervisory control station demotes itself to a stand-by station status by sending said permission signal.   
     
     
       5. The system of claim 1, wherein said normal supervisory control station transmits said second data at an end of a period of collection of said first data from said control terminal device by said normal supervisory control station. 
     
     
       6. A method of controlling a master-slave-type control system including a common transmission passage for transmitting various data, at least one control terminal device connected to said transmission passage, a normal supervisory control station, connected to said transmission passage for supervising operations of said control terminal device, and a stand-by supervisory control station connected with said control terminal device and said normal supervisory control station only through said transmission passage for supervising operations of said control terminal device in case said normal supervisory control station is disabled, the method comprising the steps of: transmitting first data concerning information to be communicated between said control terminal device and a currently operative one of said normal supervisory control station and said stand-by supervisory control station which is currently supervising operation of said control terminal device, through said common transmission passage between said normal supervisory control station and said control terminal device;   intercepting said first data transmitted on said common transmission passage at said stand-by supervisory control station;   transmitting second data, concerning information about an internal state of said normal supervisory control station, from said normal supervisory control station through said common transmission passage to an imaginary station having a non-existent address;   intercepting said second data transmitted on said common transmission passage at said stand-by supervisory control station;   detecting an abnormality of said normal supervisory control station by said stand-by supervisory control station in accordance with said second data obtained by intercepting said second data sent to said imaginary station; and   switching from control by said normal supervisory control station to control by said stand-by supervisory control station when said abnormality of said normal supervisory control station is detected by said stand-by supervisory control station.   
     
     
       7. The method of claim 6, wherein said stand-by supervisory control station detects said abnormality of said normal supervisory control station in case of an absence of transmission of said second data from said normal supervisory control station to said imaginary station. 
     
     
       8. The method of claim 6, wherein said switching step from said normal supervisory control station to said stand-by supervisory control station is carried out by the steps of: sending a request signal from said stand-by supervisory control station to said normal supervisory control station when said abnormality of said normal supervisory control station is detected by said stand-by supervisory control station, through said common transmission passage;   sending a permission signal from said normal supervisory control station to said stand-by supervisory control station when said request signal is received by said normal supervisory control station from said stand-by supervisory control station through said common transmission passage; and   switching control for supervising operation of said control terminal device from said normal supervisory control station to said stand-by supervisory control station when said permission signal is received by said stand-by supervisory control station from said normal supervisory control station through said common transmission passage.   
     
     
       9. The method of claim 6, wherein said second data are transmitted by said normal supervisory control station at an end of a period of collection of said first data from said control terminal device by said normal supervisory control station.